This invention relates generally to a control system and method for a continuously variable transmission, and more particularly, to an electronic control system and method for a multiple range continuously variable transmission, which system and method includes electrical motors/generators precisely controllable for rotating members of the transmission at speeds corresponding to rotational speeds of an input or output connecting the members to and disconnecting the members from the input or output using mechanical clutches.
In a machine, such as a wheel loader or a track type tractor, for example, an engine supplies power for propelling the machine in the forward and reverse directions, and for powering machine implements. A transmission is coupled to the engine and transmits power from the engine to the drive train to propel the machine. It is desirable to utilize a continuously variable transmission and manage the transmission ratio to save engine power for the implements and also to provide a continuously variable power flow through the transmission to improve machine productivity. Because machines operate at relatively low speeds and in cyclical work routines, there is a need to control speed precisely and for the speed to be infinitely adjustable throughout the ranges of the transmission. Changing or shifting the range involves engaging one clutch at near synchronous speed and disengaging another clutch, and it is desirable to make the range change without interrupting the torque or rate of ratio change in the transmission.
Many known transmissions use an electronically controlled hydraulic system for varying the ratio within a range, and frictional clutches instead of mechanical clutches for changing range. Although mechanical clutches are typically more efficient, they can suffer from a shortcoming known as a xe2x80x9cfour squarexe2x80x9d lockup. Lockup is typically due to an inherent slow response of the hydraulic system to electronic control signals. When a lockup occurs, the hydraulic system usually must be dithered, resulting in a noticeable delay in range change.
Thus, it is desired to provide an electrical alternative to the known hydraulic systems for continuously variable transmission which allows use of the more efficient mechanical clutches, but which avoids the lockup problems and operational delays associated therewith.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
According to one aspect of the invention, an electronic control system for a continuously variable transmission is disclosed. The control system includes a plurality of clutch actuators adapted to be connected to clutches disposed for connecting members of the transmission to an input or output, respectively, the clutch actuators each being operable for respectively engaging corresponding of the clutches for selectably connecting the members to the input or output and disengaging the clutches for selectably disconnecting the members. The control system includes a first electrical motor/generator connected to a member of the transmission and operable in a motor mode for controllably rotating the member and in a generator mode controllably rotated by the member to generate electrical energy, a second electrical motor/generator connected to another member of the transmission and operable in a motor mode for controllably rotating that member and in a generator mode controllably rotated by that member while generating electrical energy, and a conductive path connecting the first and second motor/generators. The control system includes a sensor for sensing a speed representative of a rotational speed of the input or output, and a processor operably connected to the sensor, the motor/generators and the clutch actuators, the processor being operable for operating one of the motor/generators in the generator mode while operating another of the motor/generators in the motor mode powered by the one of the motor/generators so as to controllably rotate selected of the members of the transmission at speeds corresponding to a sensed rotational speed of the input or output for disconnecting one of the selected members from the input or output and connecting another of the selected members to the input or output.
In another aspect of this invention a method for operatively connecting components of a control system for a continuously variable transmission is disclosed. The method includes the steps of selectably connecting members of the transmission to an input or output of the transmission, utilizing a plurality of clutches adapted to be connected to a plurality of clutch actuators, the clutch actuators each being operable for respectively engaging corresponding of the clutches for connecting the members to the input or output of the transmission and disengaging the clutches for disconnecting the members therefrom, connecting a first electrical motor/generator to a member of the transmission and operable in a motor mode for controllably rotating the member and in a generator mode controllably rotated by the member to generate electrical energy, adaptively connecting a second electrical motor/generator to another member of the transmission and operable in a motor mode for controllably rotating the another member and in a generator mode controllably rotated by the another member while generating electrical energy, connecting a conductive path between the first and the second motor/generators, a sensor for sensing a speed representative of a rotational speed of the input or output of the transmission, and operably connecting a processor to the sensor, the motor/generators and the clutch actuators, the processor being operable for operating one of the motor/generators in the generator mode while operating another of the motor/generators in the motor mode powered by the one of the motor/generators such that selected of the members of the transmission are rotated at controlled speeds corresponding to a sensed rotational speed of the input or output of the transmission for disconnecting one of the selected members from the input or output of the transmission and connecting another of the selected members to the input or output of the transmission.